A drawback common to folding doors is that when the suspension bases which are the running members for suspending the folding doors approach each other for folding of the doors the doors are brought into a state similar to suspension from a point and are likely to sway sideward, thereby becoming hard to move.
For preventing such a sideward sway of the folding doors at the time of folding, prior art solutions, e.g., as disclosed in Japanese Utility Model Registration Official Gazette, No. 62-7832, have been proposed. In the device according to this prior art, running members are respectively provided with projections each directed toward and adapted to abut on the other. Guide rolls are provided on both sides of each projection in such a manner that respective tips of both projections abut on each other for keeping the doors folded roughly into the shape of a "V" while preventing the doors from folding so much as to be parallel with each other, to thus prevent sideward sway of the folding doors.
Such a device, however, has the considerable drawback that the doors are folded in the shape of a "V" opening at a large angle and not in parallel with each other and thus may be obstructive when near a space to be used as a passageway. Particularly, when a combination of a plurality of folding doors capable of moving right and left along rails are used for a partition, a width of opening of the opened partition is largely reduced as far as the doors are folded in the "V" shape and, therefore, the partition is not suitable for substantial service unless the folding doors are removed.